Turbo-machinery shafts generally require rotational mechanical balancing to avoid vibration when they are at running speed. FIG. 1 shows an exemplary known compressor and torque tube portion of a combustion turbine rotor 20, comprising a rotor shaft 22 and balancing rings 24. As is well-known, the rotor typically includes a bore 188 that extends along the rotational axis of the rotor. The bore 188 is formed during manufacturing to remove impurities that tend to form or collect near the rotational axis during the manufacturing process. The turbine section portion of the known rotor is not shown. The balancing rings' locations are often referred to as “balance planes” that are perpendicular to the rotor's rotational axis. Threaded plugs 26 are inserted into threaded bores that are arrayed about the rotor at the plane. Other methods of installing balance weights such as capturing the weight in a toothed slot, or other methods may be used in some applications.
During initial fabrication of the rotor 20 prior to initial balancing rotor vibrations are monitored during a spinning procedure. For previously operational rotors during service refurbishment prior history of monitored rotor vibration is also often utilized. For either new or refurbished rotors, the monitored vibrations are used to determine a balance weight array pattern of weight and bore locations along the balance plane that will be expected to counteract the monitored vibration. In a so-called “balance move” service procedure, the rotor is brought to a standstill and the balancing weights are installed in accordance with the previously determined balance weight array pattern. The balance move procedure is repeated iteratively, if necessary, to establish rotor balance within functional specifications. Upon completion of the balancing procedure the balancing weight mass and positions remain static until the next rotor service outage.
During turbo-machine operation, such as combustion turbine engine operation, a rotor 20 can become out of balance due to disassembly and reassembly during maintenance, normal wear of seals and other components, engaging of clutches, or thermal expansion of the rotor. If the rotor 20 out of balance condition is not so severe as to require immediate turbine engine shut down, the engine may continue to be operated until the next scheduled maintenance outage, but nonetheless at a higher than desired vibration level. If vibration levels increase beyond acceptable specifications the turbine engine may have to be shut down for balancing maintenance ahead of the next scheduled outage, resulting in an unscheduled engine service disruption.